In recent times, the use of optical fiber communications has increased dramatically, and the promise of increased signal transmission speed and clarity makes it likely that the use of optical fibers for signal transmission will continue to rise in the future. Therefore, it is likely that the amount of optical components, particularly optical fiber, being manufactured will increase in the future as optical communications systems replace communication systems based on electrical signals. Consequently, the ability reduces the costs associated with the production of optical components and, particularly, optical fiber is and will likely continue to be significant.
Germanium tetrachloride is one of the most expensive ingredients in the manufacture of optical fiber. In the process for making optical fiber, germanium tetrachloride is combusted to produce germanium dioxide which is incorporated in the optical fiber during its manufacture. However, the combustion of germanium tetrachloride is not efficient in the processes presently used to make optical fiber. As a result, a considerable amount of germanium tetrachloride as well as other forms of germanium (e.g., GeO.sub.2 particulates that are not incorporated into the optical fiber) is lost in the process, typically in the exhaust gases. Generally, the exhaust gases from the production of optical fiber contain unreacted germanium tetrachloride vapor, germanium dioxide, silicon tetrachloride, silicon dioxide, hydrochloric acid gas, and water vapor, as well as large amounts of gasses found in ambient air (e.g., nitrogen, oxygen, and carbon dioxide). Although the exhaust gas is filtered through a baghouse, this filtration only recovers a fraction of the germanium present in the exhaust gas. After filtration, the exhaust gas is directed to scrubbers which are designed to remove the hydrochloric acid from the exhaust gas. Whatever germanium is contained in the exhaust gasses entering the scrubbers is lost in the scrubber waste acid or is released with the stack gasses from the scrubber operation.
A number of methods have been devised to address the loss of germanium in optical fiber production. In one such method, multivalent cations, such as magnesium (II) ions, were used to precipitate germanium from the scrubber waste acid after neutralization. However, applicants have discovered that not all germanium is captured in the scrubber waste acid. Therefore, even if all of the germanium in the scrubber waste acid could be precipitated using multivalent cations, a significant amount of germanium would, nevertheless, be lost in the stack gasses. Furthermore, it is sometimes undesirable to neutralize the large amount of acid collected by the scrubber as practiced in this method.
A need exists for an effective method of recovering germanium from the exhaust gases produced during optical fiber manufacture. The present invention addresses this need.